Apheresis is a procedure in which an individual blood component can be separated and collected from whole blood temporarily withdrawn from a subject. Typically, whole blood is withdrawn through a needle inserted into the subjects arm and into a cell separator, such as a centrifugal bowl. Once the whole blood is separated into its various components (e.g., plasma, red blood cells, white blood cells, and platelets), one or more of the components can be removed from the centrifugal bowl. The remaining components are returned to the subject with optional fluid compensation to make up for the volume of the removed component.
One concern with apheresis systems is the amount of extra corporeal volume (ECV), or the amount of whole blood that is outside of the body during the procedure. For the safety of the donor subject and to improve the donor subject's tolerance to the procedure, the extra corporeal volume should be minimized. The limits on the ECV have created a variety of apheresis systems and separation device designs. For example, current apheresis systems typically employ either a continuous flow separation device or discontinuous flow separation device. Continuous flow separation devices do not typically accumulate separated components within the device during separation (although a container may be added external to the separation device). Conversely, blood components typically accumulate within a discontinuous separation device and are later removed or extracted from the separation device.
Another significant difference between continuous and discontinuous separation devices is the number of access ports that each have. In particular, continuous flow separation devices typically have at least 3 access ports (1 input port for the anticoagulated whole blood, and 2 component output ports), whereas discontinuous separation devices only have two ports (an inlet and an outlet).
Apheresis systems utilizing discontinuous separation devices (e.g., a two port centrifuge bowl) draw whole blood from the donor or patient through a conduit into the centrifuge bowl, where component separation takes place. When there is sufficient volume in the bowl, the drawing of fresh blood is stopped, and the unwanted components are returned to the donor or patient through the same conduit intermittently, which creates lag times and increases the overall procedure time. When the return has been completed, whole blood is again drawn from the donor or patient, and a second cycle begins. This batch process continues until the desired amount of component has been collected.